The use of plastic containers for packaging food and other items has become more prevalent since new advances in this field have allowed the production of better containers. Such containers typically consist of the product carrying portion and a lid preferably sealable to the container to preserve the freshness of the contents. When it is desired to consume the contents, the problem arises of how to easily open the container with a minimum of effort. For this reason, the lid systems used to cover the container opening usually consist of a peelable or breakable material that may be punctured or torn, or in the case, for example, of beverage cans a frangible groove section may be imprinted in the container top lid which defines a preferential zone of failure of the lid material when subjected to the opening efforts of the consumer. This system embodies, for example, the popular "zip top" opening systems typically used on beverage containers.
In review of the prior art in this area, it becomes apparent that these frangible areas are typically defined by the stamping of a groove or other indentation into the material of the lid stock, in a separate operation, prior to the attachment of the lid stock to the container. For example, in U.S. Pat. No. 3,937,349 a frangible tear area is formed before the cap is placed on the bottle 30. In U.S. Pat. No. 4,332,332 the frangible area is formed in the lid stock and then in a separate operation the lid stock is heat sealed to the container. In U.S. Pat. No. 4,640,427 the frangible tear is formed with closure 11, but closure 11 is not bonded to the container at the same time but uses threads to become attached to the container 10. In U.S. Pat. No. 4,344,472 a frangible seal is formed and then closure 10 seals the opening in port flange 30. In U.S. Pat. No. 4,284,199 a frangible area is defined at the time the entire container is formed and no cap is thereafter placed on a pre-existing container and sealed thereto. In U.S. Pat. No. 3,985,255 the frangible area is defined on the lid in a separate operation prior to placement of the lid on the container. In U.S. Pat. No. 4,586,625 the frangible area is formed before the lid is placed on the container. In U.S. Pat. No. 4,553,683 the frangible area is formed on the housing prior to placing the housing on the cup 11 and bonding it thereto. In U.S. Pat. No. 4,611,725 l a frangible area is formed on the lid prior to placement of the lid on the container. In U.S. Pat. No. 4,361,250 a frangible area on the lid is formed prior to placement of the lid on the container. The same comment also applies to U.S. Pat. Nos. 4,722,449 and 4,018,353.
Great Britain Patent 1,241,425 teaches the sealing of the lid to the container by use of a heated die but does not mention the formation of a frangible area in the lid stock. And finally, a sales brochure by Indemitsu Petrochemical Company, Ltd. discloses their Magictop.TM. plastic container wherein a frangible area is formed in the container proper, and thereafter the container is sealed with a cover not having a frangible area.
In review of the above publication and patents the complexity of fabricating an openable lid and sealing the openable lid to a container becomes apparent. A method and apparatus need be developed that simplifies the manufacturing process necessary to yield an openable container.